Olivier Aubin-Mercier is currently training at H2O MMA and the Tristar Gym in Montreal. Olivier Aubin-Mercier is also one of the MMA coaches at the Ultimaction gym in Drummondville, Quebec. In 2012, Aubin-Mercier was considered the best prospect in Quebec MMA according to a La Voix des Guerriers survey.

With a perfect 4-0 amateur record, Olivier Aubin-Mercier made his professional MMA debut October 21st against Guy Poulin (1-0 before the fight). He won the fight by rear-naked choke in under a minute. His second MMA fight had a similar result, as Aubin-Mercier won by rear-naked choke in only 70 seconds. On November 30th 2012, Aubin-Mercier improved to 3-0 with another first round rear-naked choke. After landing multiple knees to Jordan Jewell's body, Aubin-Mercier got a takedown and quickly secured the choke. He would pick up another win before joining The Ultimate Fighter.

Aubin-Mercier would make it to the final of the Ultimate Fighter Canada vs. Australia but would lose a split decision to Chad Laprise. Following the first loss in his career, Aubin-Mercier returned to winning form in picking up his first UFC win as well as a Performance of the Night bonus against Jake Lindsey, submitting "The Librarian" in the second round via keylock.